112745

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <math.h>
#include <climits>

//#pragma GCC optimize("O3, unroll-loops");

#include <list>
#include <map>
#include <set>
#include <queue>
#include <unordered_map>
#include <unordered_set>

//#include <chrono>
//#include <fstream>
//#include <bits/stdc++.h>

#define mp make_pair
#define pb push_back
#define eb emplace_back
#define x first
#define y second
#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,b,a) for (int i = (b) - 1; i >= (a); i--)

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pi;
typedef pair<ll, ll> pl;
typedef vector<int> veci;
typedef vector<bool> vecb;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;

const int INF_I = 1e9;
const ll INF_LL = 1e18;

int main() {
    /*ifstream cin("in.txt");
    ofstream cout("out.txt");
    auto start_time = chrono::high_resolution_clock::now();*/

    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);


    int n, k;
    cin >> n >> k;
    veci a(n);
    for (int i = 0; i < n; i++)
        cin >> a[i];

    vector<ull> sum(n);
    sum[0] = a[0];
    for (int i = 1; i < n; i++)
        sum[i] = sum[i - 1] + a[i];

    vector<ull> p(n);
    for (int i = k-1; i < n; i++)
        p[i] = max(p[i - 1], sum[i] - (i >= k ? sum[i - k] : 0));

    vector<ull> s(n);
    for (int i = n - k; i >= 0; i--)
        s[i] = max(s[i + 1], sum[i + k - 1] - (i > 0 ? sum[i - 1] : 0));

    ull minn = ULLONG_MAX;
    for (int i = 0; i < n; i++)
        minn = min(minn, max((i > 0 ? p[i - 1] : 0), (i + k < n ? s[i + k] : 0)));

    cout << minn << "\n";

    /*auto end_time = chrono::high_resolution_clock::now();
    chrono::duration<double> duration = end_time - start_time;
    cout << duration.count() << "\n";
    cin.close();
    cout.close();*/
    return 0;
}